Engines with variable displacement operation are well known in the art for providing increased fuel efficiency by deactivating cylinders during operation modes requiring reduced engine output. Such designs may also incorporate cam profile switching (CPS) to enable high or low lift valve train modes which correspond to increased fuel efficiency during high and low engine speeds, respectively. Further, in CPS systems, variable displacement engine (VDE) design may be supported through a no-lift cam profile that deactivates cylinders based on engine output needs.
However, a potential issue with variable displacement engines may occur when transitioning between the various displacement modes, for example, when transitioning from a non-VDE (or full-cylinder) mode to a VDE (or reduced cylinder) mode, and vice-versa. Specifically, the transitions can significantly affect the manifold pressure, engine airflow, engine power, and engine torque output. For example, these transitions may produce disturbances in engine torque output and may increase noise, vibration, and harshness (NVH) of the engine.
The inventors herein have recognized the above issue and identified an approach to at least partly address this issue. A method comprises during a first condition, operating the engine with a single cylinder deactivated and remaining cylinders activated with a first intake duration, during a second condition, operating the engine with the single cylinder deactivated and the remaining cylinders activated with a second intake duration, and during a third condition, operating the engine with all cylinders activated. In this way, a four-cylinder engine (for example) may be operated with a three-cylinder mode providing improved fuel economy.
For example, an engine may comprise four cylinders wherein only a single cylinder includes a deactivation mechanism. The remaining three cylinders may include at least one intake valve that may be actuated between an open position and a closed position via one of two cam lobes. A first cam lobe may provide a first intake duration at a first valve lift, and a second cam lobe may provide a second intake duration at a second valve lift. Herein, the first intake duration may be longer than the second intake duration. Further, the first valve lift may be higher than the second valve lift. The engine may include a cam profile switching (CPS) system to switch between the first cam lobe and the second cam lobe during different engine operating conditions. In one example, if the engine is operating under light loads, the single cylinder may be deactivated and the remaining three cylinders may be operated such that their intake valves are actuated by their respective second cam lobes. In another example, if the engine is operating under medium loads, the single cylinder may be deactivated and the remaining three cylinders may be operated such that their intake valves are actuated by their respective first cam lobes. During very high engine loads, the engine may be operated in a non-VDE mode and the first cylinder may be activated while the remaining three cylinders may be operated such that their intake valves are actuated by their respective first cam lobes. Thus, during low engine load conditions, the engine may be operated in three-cylinder mode with shorter intake durations, and during medium engine load conditions, the engine may be operated in three-cylinder mode with longer intake durations.
In this way, an engine may be primarily operated in a three-cylinder VDE mode over a wider range of engine loads by varying intake durations and intake valve lifts. The engine may be transitioned to full-cylinder mode only during very high engine loads which may occur relatively sporadically. Therefore, a number of transitions between the three-cylinder VDE mode and the full-cylinder mode during a drive cycle may be significantly decreased. Further, smoother engine operation may be attained by reducing the number of transitions between VDE and non-VDE modes. Additionally, by operating the engine largely in the three-cylinder VDE mode, fuel consumption may also be reduced, providing a reduction in maintenance costs.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.